This invention relates to a viscose rayon filament yarn directly obtainable from viscose dope by a series of rapid, very simple and continuous treatments and procedures. Such yarn is quite excellent in uniformity, much lower than the viscose rayon filament yarns produced by the conventional continuous spinning process in terms of the free sulfur content in yarn and therefore excellent in resistance to deterioration with time. The yarn is thus light resistant, weather resistant and the like. This invention also relates to a process for producing said yarn.
Hitherto, many manufactures of viscose rayon filament yarn have produced yarn by a divided process in a non-continuous process (referred to as a divided process, hereinafter). The divided process comprises winding up the spun yarn in a vessel or on a reeling tube as a cake or a spool and then scouring, drying and finishing this yarn package at a separate place.
Obviously, the divided process has the following two undesirable effects. The first disadvantage consists in that the spun yarn package has to be taken out of the spinning zone, transported to the scouring zone and again arranged in the latter zone. The second disadvantage consists in that the yarn is subjected to the finishing treatment in the bulky state.
For these reasons, the industry necessitated many workers. The yarn formed by this divided process had a fault that a certain property has a tendency to be greatly changed along the longitudinal direction of yarn. The yarn formed by the divided process is subjected to treatments subsequent to scouring in the bulky state, so that the differences introduced in the spinning or drying step remained as a quality difference along the longitudinal direction of the finished yarn. Therefore, the manufacturers of viscose rayon filament have searched for a continuous spinning process over many years with the aim of obtaining a yarn of high uniformity and high working productivity and, as a result, filament yarns continuously spun from viscose, processes for producing them and apparatuses therefor have been provided. By these disclosed continuous processes, a dope of viscose is passed through a spinning nozzle to form it into filaments, after which it is continuously fed into the next step in the form of filaments where it is subjected to impregnating treatment, chemical treatment, heat treatment and drying treatment and, if necessary, a finishing agent is added and the filaments are heated.
Since the filaments just after being spun naturally contain a large quantity of harmful substances, the scouring treatment for eliminating these harmful substances, but takes a long period of time. Accordingly, a means which is sized as small as possible, can contain as large as possible amount of long filaments and can make the treatment adequately progress, has been desired. For the purpose of fulfilling these functions, a process which comprises making the yarn go ahead or accumulating it on a moving net either spirally or linearly by the use of reel or roll and applying the above-mentioned treatment while the yarn moves, or some like methods have been practised.
In contrast to the conventional divided process in which a long period of time may be consumed for the treatment because a large quantity of filaments are treated in a tightly congregated form (cake or spool), the time period allowable for the scouring treatment in the continuous spinning process is restricted from the standpoint of cost and at most conducted within several minutes. Thus, the greatest interest has been attached to ways how to eliminate the harmful substances effectively from inside of each filament within a very short time period of treatment.
Thus, there have been proposed a number of processes for producing viscose rayon filament yarn by the continuous spinning finishing method, which are mentioned in the following papers, for example:
(1) The Nelson continuous spinning process is mentioned in Rayon Textile Monthly, Vol. 28, December, pp. 59-62 under the title of "Nelson Continuous Viscose Rayon Spinning Process". This technique is characterized by using only water for scouring yarn.
There are known a number of continuous spinning finishing processes using chemical solutions according to the mode of scouring in the divided process, of which typical examples will be mentioned in (2)-(5).
(2) The Kuljian continuous spinning process in which a plurality of rolls are combined with slight inclinations to give a single reel and the scouring treatment with a chemical solution is practised while feeding the yarn by the rotation of rolls is mentioned in Textile World, Vol. 97, December, p. 157 (1947).
(3) The Industrial Rayon continuous spinning process in which the scouring treatment with a plurality of chemical solutions is carried out while advancing the yarn by the use of a reel having alternately convexed arms for individual chemical solution steps is mentioned in Walter Fred Knebush: Japanese Pat. No. 133,871. It is well known in this field of industry.
(4) A process in which the treatment with chemical solutions is carried out with a machine so constructed that the chemical solution treatment roll is divided into many zones in contact with the yarn and arranged so that the circumferential arc of the treating roll comes into contact with the spiral of yarn is mentioned in Sidney Wallen Barker: British Pat. No. 32,903 (1960).
(5) A process in which one scouring drum is combined with a plurality of driving rolls, one driving roll advances only one yarn and during such time all the other yarns are subjected to chemical solution treatment in one scouring drum is disclosed in Japanese Patent Publication No. 46,927/1978, published on Dec. 18, 1978.
In the Nelson process using only water for scouring yarn, the yarn is advanced, while wound up on two rolls, as the rolls rotate owing to the inclination of the two rolls. Acid treatment is carried out so as to complete the coagulation and regeneration in this time period. After which washing with water and drying are carried out. Desulfurizing and bleaching which are used in the divided process are not carried out to simplify the process. Since the equipment and operation costs can be reduced in this process, it is suitable for obtaining a filament yarn of small denier. However, the yarn formed contains large quantities of metals, sulfur and their compounds and particularly free sulfur, so that the yarn has a fault in that it undergoes a quality change with time or its strength, elongation or whiteness drops with time by the action of light or heat. Further, desulfurizing and bleaching have to be carried out otherwise before the yarn can be practically used (for this reason, the yarn produced by this process is also called "unscoured yarn"). Because of these faults, fabric manufacturers were extremely hesitant to produced by the Nelson process in some usages, and yarn manufacturers provided the above-mentioned processes (2)-(5) in order to apply the divided type of scouring processes (at high equipment cost) to supply a product acceptable to the industry. In these continuous spinning processes, naturally the scouring process for viscose rayon filament yarn of the divided system is used so that an apparatus of a larger scale is required and the handling is unavoidably complicated: Furthermore, the many kinds of treating solutions mix with one another when the yarn moves from one chemical solution treatment zone to another chemical solution treatment zone so as to reduce the efficiency of treatment, of which prevention necessitates much consideration.
With the aim of overcoming these disadvantages, an attempt was made to provide a barrier such as flange or ditch on the roll surface and thereby to prevent the mixing of different chemical solutions.
Although the yarn thus obtained was recognized to contain smaller quantities of metallic components such as zinc, lead, iron and the like and to have a higher whiteness, it was still not free from the character that mechanical properties, dyeing properties and whiteness deteriorate with time.
Since the yarns obtained by these conventional processes such as the Nelson process, the Industrial Rayon process, the Kuljian process etc. are good in the uniformity of width in the longitudinal direction of yarn and of dyeing, and they have been accepted in the fields of fabrics etc. However, the endeavors before the accomplishment of this invention was only exerted to the application of the divided process, the continuous processes or to the simplification from the viewpoint of cost. No consideration was given heretofore to the chemical and physical changes of free sulfur inside each filament in the course of the continuous spinning and scouring process which takes at most several minutes, so that filament yarn did not improve in the above-mentioned points till the present invention.
In this invention, however, it was evidenced that a novel yarn product having unique properties unattainable by the conventional processes can be obtained by a scouring technique using only water.
In order to further deepen the understanding regarding the yarn product of this invention, however, it is desirable to mention here the properties of the yarn obtained by divided process and the yarns obtained by the above-mentioned conventional continuous spinning finishing processes.
Whatever the process employed, it is well known that some quantity of sulfur remains in the filament yarn formed from viscose and the sulfur makes the processing of yarn in the course of its use difficult. For this reason, the yarn obtained by divided process is treated with a solution of sodium sulfide to remove the fine sulfur particles contained inside the yarn in the form of polysulfide. Further, the yarn is treated with sodium hypochlorite (NaOCl) in order to remove metal sulfides and metal sulfates, then washed with acid, neutralized and washed with water to obtain a finished and complete yarn. At this time the amount of free sulfur remaining in the yarn is about 0.02% or less and the yarn thus obtained is excellent in resistance to deterioration with time.
On the other hand, in the continuous process, the yarn obtained by the prior technique of the Nelson process is considerably colored because the scouring process employed in the divided process is not used there and large quantities of metals, sulfur and their compounds, particularly free sulfur, remain in the yarn.
Therefore, the deterioration of properties with time by the action of environmental conditions cannot be avoided. Thus, the yarn has a fault that mechanical properties such as strength, elongation and the like, or whiteness decrease with time by the action of light, heat or other environmental factors and, when it is put to practical use, it necessitates additional desulfurizing and bleaching. That is why such yarn is called "unscoured yarn".
In contrast to the Nelson process, the yarn obtained by processes (2)-(5), which are subjected to chemical solution treatments such as desulfurizing and bleaching, have a reduced content of metallic components such as zinc, lead, iron and the like and are improved in whiteness. Nevertheless, a sufficient desulfurizing cannot be done within the allowable time period of treatment. This is because the use of chemical solutions increases the number of divisions of treatment owing to which the time period allocated to each chemical solution treatment is restricted. In addition, the continuous processes differs from the divided process in that the time period allowable to the whole treatment is at most several minutes or less from the viewpoint of equipment cost. As the result, the yarn obtained still retains the character that mechanical properties, dyeing properties, whiteness and the like deteriorate with time. Yarn having excellent resistance to deterioration with time has not heretofore been obtained.
Therefore, all the disclosed yarns formed by continuous spinning finishing processes have a high content of free sulfur, and this value often exceeds 0.1% ( based on the weight of yarn). For example, a value of 0.1% is mentioned in a publication dealing with yarns obtained from PNSH (name of a continuous spinning machine) in USSR. An analysis of disclosed yarns obtained by a continuous spinning finishing process revealed that even the lowest value of free sulfur was 0.06-0.07%. As has been mentioned above, at even this value the resistance to deterioration with time is not satisfactory.
For this reason, production of a yarn from which free sulfur has been removed effectively by a continuous spinning finishing process was considered impossible and it was believed that the amount of free sulfur has to be lowered to about 0.02% in order to obtain a continuously spun filament yarn comparable to the yarn produced by the divided process in regard to resistance to deterioration with time. However, it was found that the novel viscose rayon filament of this invention based on the productive means mentioned later has a unique character in point of free sulfur content which was considered insufficient hitherto in connection with resistance to deterioration with time. This finding offers a grounds to the characteristic feature of this invention.
The objects of this invention will be obvious from these facts. Thus, it is an object of this invention to provide a process for producing viscose rayon filament yarn having comparable resistance to deterioration with time to that of filament yarn produced by the divided process, by using a very simple means. It is another object of this invention to provide a process for producing a filament yarn which resembles the yarn obtained by the divided process in the above-mentioned properties, but having a very high uniformity in the longitudinal direction of yarn. It is yet another object of this invention to obtain a yarn having particularly useful properties when used in the fields other than the conventional fields of use of viscose rayon filament yarn, such as outer garments. It is still another object of this invention to provide a process for obtaining, economically and in high yield, a filament yarn having a harmful substance content suppressed under the allowable limit by a quite ordinary operation. Other objects of this invention will be apparent from the descriptions given below.